DESCRIPTION: The Objective of the proposed research is to develop a new technology for fiber optic chemical sensors that can be applied to invasive biomedical measurements. The chemical sensing element is a thin (ca. 5 micrometers) film of a polymer coated onto the tip of an optical fiber. The polymer will be toughened, lightly crosslinked polystyrene chemically modified so that it swells and changes refractive index as a function of concentration of an analyte. Changes in refractive index will be measured as changes in the intensity of light reflected at the fiber/polymer and polymer/sample interfaces using a referenced, time-resolved measurement. The light source will be a laser diode pulsed at a frequency on the order of 10kHz. The proposed sensing technology is expected to be stable with respect to calibration since it involves a very thin layer of polymer and response times will be short. The proposed approach involves neither photoexcitation nor photodegradation as other fiber optic chemical sensors usually do and can be applied in the near infrared range in order to take advantage of technology developed for fiber optic communications. It will initially be developed with 100/140 micrometer core/cladding glass-on-glass optical fibers that can be miniaturized further for invasive measurements. A single inexpensive instrument is capable of several measurements as long as the length of fiber between the source and each measurement site differs. The polymer coating which is a toughened polystyrene formulation developed by the group can undergo repeated swelling and shrinking cycles without degrading mechanically and will be derivatized with an amine functional group to make a PH sensor, a dicarboxylate group to make a calcium sensor and boronic acid to make a sensor that responds to carbohydrates.